1. Field of the Invention
The present invention relates to a time-division multiplex switching network, particularly a pulse code modulation (PCM) time-division multiplex switching network comprising switching units designed as time stages operating blocking-free and respectively effecting the chronological and spatial assignment of time channels employed on time-division multiplex lines for a incoming transmission direction to a time-division multiplex lines for an outgoing transmission direction, a respective plurality of time-division multiplex lines being connected to the switch units, in which time-division multiplex switching network at least two one-stage switching network portions are formed which respectively embrace as many switching units are switching network portions and in which the time-division multiplex lines for the incoming transmission direction connected to the switching units are also respectively connected to one input of a switching unit of each other switching network portion.
2. Description of the Prior Art
In view of possibilities of increase, such a time-division multiplex switching network offers advantages in comparison to multi-stage switching matrix arrays constructed of the switching units. Such switching matrix arrays as are two-stage, in particular, on the one hand produce a greater delay time in the through-connection of the signal and, on the other hand, are sensitive to out-of-balance loads, i.e. that when, proceeding from a switching unit of a first stage, priority connections to time-division multiplex lines which are connected to one and the same switching unit of a second stage are to be produced at the same time, a blockage can occur because of the limited number of intermediate lines. This out-of-balance load sensitivity no longer exists given three-stage switching matrix arrays but, instead, the delay time through the switching matrix array is even greater and, in addition, correspondingly more connection commands are required for the through-connection of the channels.
In a known time-division multiplex switching matrix array of the type initially mentioned, equivalent outputs of the switching units within the individual switching network portions are connected to one another and are connected to a respective time-division multiplex line for the outgoing transmission direction. Because of the specified type of connection of the time-division multiplex lines for the incoming transmission direction to the switching units, therefore, given failure of a switching network portion, the traffic heretofore routed over that portion can be sequenced via the remaining, intact switching network portions with only relatively slight blockage.
Thereby, the outputs of the switching units connected to one another are called tri-state outputs by means of which the binary values "1" and "0" as well as the quiescent state can be represented by three different signal levels. Whereas it is guaranteed in proper operation that two outputs connected to one another do not simultaneously assume the active condition during a time slot, in the activation phase, it can nonetheless occur which, when the binary value "1" is supplied from one input and the binary value "0" is supplied from the other input, can lead to destruction of the appertaining components of the switching units which form the outputs. It can also occur in the activation phase that the emission of free-channel code words transmitted during non-seized time phases does not properly operate, the emission normally proceeding from that switching unit from which a previously-existing connection had been triggered during the appertaining time slot.